Certain displays, image sensors and even the human eye have a non-linear transfer function. In order to compensate for this non-linearity a substantially inverse correction function is applied. This compensation stage is also known as gamma (γ) correction.
The gamma correction function can be represented by the following equation: Y(X)=X1/γ, wherein X represents a non-compensated pixel value (for example brightness or contrast), Y is the gamma compensated pixel value and γ is the gamma factor that is characteristic of the non-linear transfer function that is compensated by the correction function.
Digital systems and digital image conversion methods use an approximation of the gamma correction function in order to perform gamma compensation. One method includes applying a linear approximation of the gamma correction function for a certain range of brightness levels while applying a non-linear approximation of the gamma correction function for another range of brightness levels. Another solution involves storing information representative of multiple gamma correction curves in a memory unit, selecting one of the curves in response to the kind or purpose of the image being gamma compensated and applying a linear function on the selected information to provide gamma compensated pixel information. The following patents and patent applications, all being incorporated herein by reference, illustrate some prior art method and devices for applying gamma compensation: U.S. Pat. No. 5,473,373 of Hwung et al., titled “Digital camera correction system for low, medium and high intensity video signals, with linear and non-linear correction”, European patent application EP0757477A2 of Tanji et al., titled “Video signal processing and video camera”, and Japanese patent application JP1993000013588 OF Asano titled “Gamma correction for digital image”.
There is a need to provide an efficient method and device for performing gamma corrections, especially for low-brightness levels.